Which of these numbers is composite? ${5,\ 39,\ 41,\ 67,\ 83}$
Solution: A composite number is a number that has more than two factors (including 1 and itself). 5, 41, 67, and 83 each have only two factors. The factors of 39 are 1, 3, 13, and 39. Thus, 39 is the composite number.